Communication is controlled centrally by a network In a Long Term Evolution (LTE) system, that is, both uplink and downlink data of a User Equipment (UE) are controlled by the network to be transmitted and received. In this mode, communication between one UE and another UE is forwarded and controlled by the network, and there is no direct communication link between the UE and the other UE, where data transmission between the UE and the network can be referred simply to as Device to Network (D2N) transmission.
In future development of a mobile communication system, in order to better satisfy a user demand, and to improve the efficiency of exchanging information between the devices, the mechanisms of Device to Device (D2D) discovery and Device to Device (D2D) communication have been introduced.
The D2D discovery mechanism is a direct discovery mechanism between two devices proximate to each other. Both of the D2D discovery devices may be online devices or may be offline devices, or one of the devices may be an online device, and the other device may be an offline device. The online device refers to a device located inside a coverage area of the network (e.g., a Third-Generation Partner Project (3GPP) network) and operating over a spectrum resource of the network is accessible. The offline device refers to a device located outside a coverage area of the network (e.g., a 3GPP network), or located inside the coverage area of the network but operating over a dedicated spectrum.
At present, air interface resources of D2D discovery are allocated in two modes, where one of the modes is the common resource pool mode in which the UEs are configured with the same air interface resources over which D2D discovery data are transmitted in some area, and the data transmitting UEs can transmit the data in some detection and avoidance mechanism, and the common resource pool is controlled by an evolved Node B (eNB) if the devices are online, or the common resource pool may be pre-configured, or may be controlled by a central control node, if the devices are offline; and the other mode is the dedicated resource mode in which a dedicated D2D transmission resource (i.e., an air interface resource) is allocated for each UE by pre-configuring the dedicated D2D transmission resource or by a central control node configuring the dedicated D2D transmission resource (which is controlled by the eNB if the UE is online).
Here the central control node is a UE or a network element capable of controlling resources, which can be referred to as a Central Node (CN) or a Central Element (CE).
D2D communication is allowed to be performed directly between devices proximate to each other. For the sake of a convenient description, a direct communication link between Device to Device (D2D) UEs can be referred to as a D2D link, and a cellular communication link between the network and the D2D UE can be referred to as a D2N link. FIG. 1 illustrates a schematic diagram of D2D communication.
Both of the D2D communication devices can be online or offline, or one of the devices can be online, and the other device can be offline.
There are the following three typical D2D communication scenarios:
In a first scenario, there is one-to-one communication between D2D UEs.
In a second scenario, one device transmits the same data once to all the devices in a communication group (group communication).
In a third scenario, one device transmits the same data once to all the proximate devices (broadcast communication).
Here one-to-one communication between D2D UEs is generally applicable to social and other applications, and the group and broadcast communication scenarios are generally applicable to fire fighting, rescuing, antiterrorism, and other public security applications.
At present there are generally two resource allocation modes for D2D communication, i.e., the common resource pool mode and the dedicated resource mode, which are particularly similar to the resource allocation modes for D2D discovery.
Different D2D transmission resource demands of different D2D services have not been taken into account in existing D2D resource allocation (including D2D discovery resource allocation and D2D communication resource allocation), and by the UE selecting a D2D service transmission resource.